Photographic material as referred to herein may comprise film, paper or any other photosensitive material and may produce a black and white or colour image.
Silver halide photographic material is well known and is processed to generate an image by passing the material through a development stage followed by a series of baths or tanks to stabilise and provide permanence to the image. The baths convert and remove unwanted materials from the photographic layers which would interfere with the quality of the final image. In a typical colour system the development stage is followed by a bleach stage to oxidise the developed silver to a form which can be dissolved by a fixing agent, either in the same bath/tank or in a separate bath/tank. The silver removal stage is followed by a washing stage using a wash solution or a stabilisation stage. These stages remove any residual chemicals from the material.
At each stage the solutions must be replenished.
Normal replenishment refers to replenishment made by a single "made-up" solution prepared by mixing concentrated parts with water in a separate replenisher tank outside the processing tank itself The concentrated parts are supplied by photographic manufacturers in a kit consisting of one or more concentrated solutions such as those for Kodak RA Prime Developer replenisher which currently consists of three parts A, B and C.
Direct replenishment (D-rep) refers to replenishment by separate concentrated parts plus a water part supplied directly into the processing tank. For Kodak Ektacolor SM developer replenisher this consist of three parts A, B and C plus a water parl These are metered into the processing tank, each with a separate pump. It is clear that more or less than three parts can also be used.
In direct replenishment plus cross-over wash the water part that would have gone directly into the first processing tank is now used to rinse the paper in the crossover between the first and second processing tanks. Some of the rinse water and the washed out components pass back into the first processing tank.
The cross-over can be between any two stages of a photographic process, which could contain developer, bleach, fix, bleach-fix, wash, stabiliser, reversal bath, conditioning bath, amplification bath or, intensification bath, etc.
When processing photographic material it is necessary for the material to pass through several different chemical solutions as described above. In conventional processors with tanks in series as the material passes from one solution to another the chemicals from a first solution are carried over by the emulsion layers of the sensitised material to the next solution. This causes seasoning of the next solution which can lower its effectiveness, particularly for the bleach-fix in the case of rapid processing. In addition carry-over of bleach-fix into the wash reduces the wash efficiency and increases the wash replenishment rate.